1. Field of the Invention
The present invention relates to an oxidation catalyst for purifying an exhaust gas, which oxidizes particulates and hydrocarbons contained in an exhaust gas of an internal combustion engine to purify the gas.
2. Description of the Related Art
Conventionally, for oxidizing particulates and hydrocarbons contained in an exhaust gas of an internal combustion engine to purify the gas, an oxidation catalyst composed of a perovskite-type composite metal oxide is known.
As a perovskite-type composite metal oxide used as the oxidation catalyst, for example, a composite metal oxide is known which is represented by the general formula: AB1-xCxO3, wherein A is at least one metal selected from the group consisting of La, Sr, Ce, Ba and Ca; B is at least one metal selected from the group consisting of Co, Fe, Ni, Cr, Mn and Mg; and C is Pt or Pd (see Japanese Patent Laid-Open No. 7-116519).
Further, as a perovskite-type composite metal oxide used as the oxidation catalyst, for example, a composite metal oxide is known which is represented by the general formula: CexM1-xZrO3, wherein M is at least one metal selected from the group consisting of La, Sm, Nd, Gd, Sc and Y; and 0.1≦x≦20 (Japanese Patent Laid-Open No. 2003-334443).
However, the conventional perovskite-type composite metal oxides have inconveniences of having a high oxidation temperature for particulates and high boiling point hydrocarbons, and moreover, not providing a sufficient catalyst activity therefor.